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A.'SCHM|DT.

SPARK PLUG.

APPLICATION msn Nov.22; 1917.

Patented ot.- 12,1920.

' cicmnws UNITEDI STATES yin.'ri-:KANT oFFicE.

ALBERT sCImIDT. or lIsLINT, MICHIGAN, AssIGNoR To CHAMPION lIGNITIoN CoMrANY, yor FLINT, MICHIGAN, A CORPORATION or MICHIGAN.

SPARK-PLUG;

y y Specification of Letters Patent." Patented Oct, 12, 1926;

limitation flied4 Nvember' 2,2, i917. serial No. 203,295'.

'- of yMichigan, have invented certain new and useful Improvements in Spark-Plugs, of

which the following is a specification, ref-r` erence being lhad therein't'o the"- accompanying` drawings. v n

he invention relates to spark-plugs and has moreparticular reference to a vconstruction designed for use in high-speed motors. In the present state of the art great difficulty has been experienced in connection with the using of spark-plugs on high-speed motors from one or the other of two opposed conditions; first, there is the difficulty of pre-ignition roccurring when the plug is too hot either through residual flame in the plug `chamber or the heating of some part ofthe surface to ignition temperature or from other causes not known. The other difficulty is where the plug `is too cool and short circuiting occurs through carbon deposits on the insulating surface. Most attempts that have been made to cure the first difficulty will introduce the second, and vice versa.

It is the obj ectof the present invention to kavoid both difficulties, which is accomplished, first, by maintaining all the large masses of they plug and the space which may contain burning gas at a temperature below the ignition point; second, by maintaining a zone in the insulating surface exposed to high temperature sufficient to burn off or prevent the formation of carbon deposits, and which nevertheless will lose its temperature during the introduction ofthe explosive gas so ask to prevent pre-ignition. This I have accomplished by the construction as hereinafter setfortli.

In the drawings:

Figure 1 is a longitudinal section through a plug embodying my invention;

Fig. 2 is a cross-section on line 2 2 Fig. l.r

' A is the outer metallic casing of the plug, B the insulated electrode and C the insulator therefor. This insulator, instead of e projecting into the explosion chamber, to a ointadjacent to the spark gap, is arranged in the outer portion of the casing which is comparatively cool. VAs shown, the insulator is in a portion of the outer casing A beyond the nipple A which screws into the Water-jacket ofthe engine, and the point ofcontact with the electrode Bas] well asf ywith the outer casing is still 'further re-` moved. This results in a skirt-like inward projection of the insulator separated both from the electrode and the outer casing, and the inner edge of the skirt is vtaperedv to a thin edgef D. Adjacent to this thin edge the vspace betweenv the insulator andj the outer casing is Contracted to form an annular nary row slot E through `which the gases are compelled to travel at high velocity. In rear of this point the skirt is increased in thickness to enlarge the mass thereof for the absorption and conductionaway of heat imparted thereto, as indicated at F. kThe electrode B is preferably formed of relatively large cross-section increasing from the sparking point toward the point of bearing upon the insulator, as 'indicated at G. II is a bushing for securing the insulator within the casing A, which bushing is shown as permanently engaging an enlargement I of the insulator and also as sealing against a shoulder J on they casing.

With the constructionV asy thus far described, when the plug is in operation the compressed gases will be forced through the restricted slot E into theV larger chamber K whicliis between the skirt and the outer casing. The high velocity of movement is sufficient to sweep clear any deposit which might occur at the point of contraction. The knife-edge D is exposed to the com bustion heat and on account of its relatively small mass will attain a temperature too high for the deposit of carbon thereon, but as soon as combustion ceases the larger mass in the skirt in rear of the edge D vwill absorb the heat. The effect is therefore to insure cooling of the knife-edge before explosive gases are compressed thereagainst and the temperature of the skirt and casing A in the portions thereof adjacent to the chamber K is too low to permit the conis maintained and pre-ignition is guarded against.

seated upon the bushing H and having a 105 wrapping of mica or other insulating material M for bridging the joint between the outer and inner insulators. A heat-radiat ing member N is also placed on the shank of the electrode beyond the outer insulator 110 vtinu'ance of flame therein. Thus insulation 100 L, and a clamping nut O engaging a threaded end portion P of the shank is provided for securing the electrical connections.

What I claim as my invention is:

l. In a spark-plug, the combination with a casing and an electrode, of an insulator contacting with said electrode and casing ata point beyond the range of intense heat and provided with an inwardly-extending skirt terminating in an annular thin edge which is exposed to the more intense heat, the space between said skirt and casing having a restriction adjacent to said thin edge to increase the velocity of gases passing therethrough.

2. In a spark-plug, the combination witha casing and an electrode therein, of an insulator for said electrode having a portion contacting therewith and with the outer cas-` ing at a point beyond the range of intense heat, said insulator also having an inwardlyextending skirt portion terminating in a thin edge which is exposed .to the more intense heat, and a shoulder on said casing forming an annular restricted passage ad jacent to said thin edge with a larger cha-mber beyond the same, for the purpose described.

3. In a spark plug, the combination with a casing, of a bushing engageable with said casing, an electrode, an insulator arranged between said electrode and bushing, a second insulator surrounding a portion of said electrode and seated upon said bushing, and insulating material between said electrode and insulators and bridging the joint between the latter.

In testimony whereof I aflix my signature.

ALBERT SCHMIDT. 

